Extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae is isolated from a patient with a healthcare-associated UTI. The ESBL enzymes are most accurately characterized as:
- A Class B metallo-beta-lactamases that require zinc cofactors and hydrolyze carbapenems
- B Class A serine-beta-lactamases (TEM, SHV, CTX-M derivatives) encoded on transferable plasmids that hydrolyze broad-spectrum cephalosporins and monobactams but are inhibited by clavulanate ✓
- C Class C AmpC cephalosporinases that are chromosomally encoded and resistant to clavulanate inhibition
- D Outer membrane porin mutations that reduce permeability to all beta-lactams
Correct answer: B. Class A serine-beta-lactamases (TEM, SHV, CTX-M derivatives) encoded on transferable plasmids that hydrolyze broad-spectrum cephalosporins and monobactams but are inhibited by clavulanate
Explanation
ESBLs are plasmid-encoded, class A serine-beta-lactamases derived mostly from TEM-1, SHV-1, or CTX-M-type ancestors by point mutations expanding the active site. They hydrolyze oxyimino-cephalosporins (ceftriaxone, cefotaxime, ceftazidime) and aztreonam but are characteristically inhibited by clavulanic acid — the basis of the double-disc synergy test for ESBL phenotypic detection. CTX-M-15 is now the predominant ESBL worldwide. Carbapenems remain active against ESBLs unless combined with porin loss.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.